The following documents are hereby incorporated by reference: U.S. Pat. No. 5,231,074, issued on Jul. 27, 1993, and entitled xe2x80x9cPreparation of Highly Textured Oxide Superconducting Films from MOD Precursor Solutions,xe2x80x9d U.S. Pat. No. 6,022,832, issued Feb. 8, 2000, and entitled xe2x80x9cLow Vacuum Process for Producing Superconductor Articles with Epitaxial Layers,xe2x80x9d U.S. Pat. No. 6,027,564, issued Feb. 22, 2000, and entitled xe2x80x9cLow Vacuum Process for Producing Epitaxial Layers,xe2x80x9d U.S. Pat. No. 6,190,752, issued Feb. 20, 2001, and entitled xe2x80x9cThin Films Having Rock-Salt-Like Structure Deposited on Amorphous Surfaces,xe2x80x99 PCT Publication No. WO 00/58530, published on Oct. 5, 2000, and entitled xe2x80x9cAlloy Materials,xe2x80x9d PCT Publication No. WO/58044, published on Oct. 5, 2000, and entitled xe2x80x9cAlloy Materials,xe2x80x9d PCT Publication No. WO 99/17307, published on Apr. 8, 1999, and entitled xe2x80x9cSubstrates with Improved Oxidation Resistance,xe2x80x9d PCT Publication No. WO 99/16941, published on Apr. 8, 1999, and entitled xe2x80x9cSubstrates for Superconductors,xe2x80x9d PCT Publication No. WO 98/58415, published on Dec. 23, 1998, and entitled xe2x80x9cControlled Conversion of Metal Oxyfluorides into Superconducting Oxides,xe2x80x9d PCT Publication No. WO 01/11428, published on Feb. 15, 2001, and entitled xe2x80x9cMulti-Layer Articles and Methods of Making Same,xe2x80x9d PCT Publication No. WO 01/08232, published on Feb. 1, 2001, and entitled xe2x80x9cMulti-Layer Articles And Methods Of Making Same,xe2x80x9d PCT Publication No. WO 01/08235, published on Feb. 1, 2001, and entitled xe2x80x9cMethods And Compositions For Making A Multi-Layer Article,xe2x80x9d PCT Publication No. WO 01/08236, published on Feb. 1, 2001, and entitled xe2x80x9cCoated Conductor Thick Film Precursorxe2x80x9d, PCT Publication No. WO 01/08169, published on Feb. 1, 2001, and entitled xe2x80x9cCoated Conductors With Reduced A.C. Lossxe2x80x9d PCT Publication No. WO 01/15245, published on Mar. 1, 2001, and entitled xe2x80x9cSurface Control Alloy Substrates And Methods Of Manufacture Therefor,xe2x80x9d PCT Publication No. WO 01/08170, published on Feb. 1, 2001, and entitled xe2x80x9cEnhanced Purity Oxide Layer Formation,xe2x80x9d PCT Publication No. WO 01/26164, published on Apr. 12, 2001, and entitled xe2x80x9cControl of Oxide Layer Reaction Rates,xe2x80x9d PCT Publication No. WO 01/26165, published on Apr. 12, 2001, and entitled xe2x80x9cOxide Layer Method,xe2x80x9d PCT Publication No. WO 01/08233, published on Feb. 1, 2001, and entitled xe2x80x9cEnhanced High Temperature Coated Superconductors,xe2x80x9d PCT Publication No. WO 01/08231, published on Feb. 1, 2001, and entitled xe2x80x9cMethods of Making A Superconductor,xe2x80x9d PCT Publication No. WO 02/35615, published on Apr. 20, 2002, and entitled xe2x80x9cPrecursor Solutions and Methods of Using Same,xe2x80x9d U.S. patent application Ser. No. 09/579,193, filed on May 26, 2000, and entitled, xe2x80x9cOxide Bronze Compositions And Textured Articles Manufactured In Accordance Therewith;xe2x80x9d and U.S. Provisional Patent Application Serial No. 60/309,116, filed on Jul. 31, 2001, and entitled xe2x80x9cMulti-Layer Superconductors And Methods Of Making Same.xe2x80x9d
The invention relates to superconductor materials, methods of making same and reactors for making same.
Multi-layer articles can be used in a variety of applications. For example, superconductors, including oxide superconductors, can be formed of multi-layer articles. Typically, such superconductors include one or more layers of superconductor material and a layer, commonly referred to as a substrate, which can enhance the mechanical strength of the multi-layer article.
Generally, in addition to enhancing the strength of the multi-layer superconductor, the substrate may desirably exhibit certain other properties. For example, the substrate may desirably have a low Curie temperature so that the substrate is not ferromagnetic at the superconductor""s application temperature. Furthermore, it may be desirable for the chemical species within the substrate to not be able to diffuse into the layer of superconductor material. Moreover, the coefficient of thermal expansion of the substrate may desirably be about the same as the superconductor material. In addition, if the substrate is used for an oxide superconductor, it may be desirable for the substrate material to be relatively resistant to oxidation.
For some materials, such as yttrium-barium-copper-oxide (YBCO), the ability of the material to provide high transport current in its superconducting state typically depends upon the crystallographic orientation of the material. For example, such a material can exhibit a relatively high critical current density (Jc) when the material is biaxially textured.
As used herein, xe2x80x9cbiaxially textured surfacexe2x80x9d refers to a surface for which the crystal grains are in close alignment with a direction in the plane of the surface or in close alignment with both a direction in the plane of the surface and a direction perpendicular to the surface. One type of biaxially textured surface is a cube textured surface, in which the primary cubic axes of the crystal grains are in close alignment with a direction perpendicular to the surface and with the direction in the plane of the surface. An example of a cube textured surface is the (100)[001] surface, and examples of biaxially textured surfaces include the (011)[100] and (113)[211] surfaces.
For certain multi-layer superconductors, the layer of superconductor material is an epitaxial layer. As used herein, xe2x80x9cepitaxial layerxe2x80x9d refers to a layer of material whose crystallographic orientation is derived from the crystallographic orientation of the surface of a layer of material onto which the epitaxial layer is deposited. For example, for a multi-layer superconductor having an epitaxial layer of superconductor material deposited onto a substrate, the crystallographic orientation of the layer of superconductor material is derived from the crystallographic orientation of the substrate. Thus, in addition to the above-discussed properties of a substrate, it can be also desirable for a substrate to have a biaxially textured surface or a cube textured surface.
Some substrates do not readily exhibit all the above-noted features, so one or more intermediate layers, commonly referred to as buffer layers, can be disposed between the substrate and the superconductor layer. The buffer layer(s) can be more resistant to oxidation than the substrate, and/or reduce the diffusion of chemical species between the substrate and the superconductor layer. Moreover, the buffer layer(s) can have a coefficient of thermal expansion that is well matched with the superconductor material.
In some instance, a buffer layer is an epitaxial layer, so its crystallographic orientation is derived from the crystallographic orientation of the surface onto which the buffer layer is deposited. For example, in a multi-layer superconductor having a substrate, an epitaxial buffer layer and an epitaxial layer of superconductor material (e.g., with the bulk of the superconductor material being biaxially textured), the crystallographic orientation of the surface of the buffer layer is derived from the crystallographic orientation of the surface of the substrate, and the crystallographic orientation of the layer of superconductor material is derived from the crystallographic orientation of the surface of the buffer layer. Therefore, the superconducting properties exhibited by a multi-layer superconductor having a buffer layer can depend upon the crystallographic orientation of the buffer layer surface.
In certain instances, a buffer layer is not an epitaxial layer but can be formed using ion beam assisted deposition. Typically, ion beam assisted deposition involves exposing a surface to ions directed at a specific angle relative to the surface while simultaneously depositing a material. In instances where ion beam assisted deposition is used to form a buffer layer, the crystallographic orientation of the surface of the buffer layer can be unrelated to the crystallographic orientation of the surface of the underlying layer (e.g., a substrate, such as an untextured substrate). Generally, however, the ion beam deposition parameters such as, for example, the ion energy and beam current, the temperature, the ratio of the number of atoms arriving at the surface relative to the number of ions coincidentally arriving at the surface, and the angle of incidence on the surface are selected so that the crystallographic orientation of the surface of the buffer layer provides an appropriate template for a layer that is deposited on the surface of the buffer layer (e.g., a layer of superconducting material).
In some instances, formation of a superconductor material involves the following steps. A solution is disposed on a surface (e.g., a buffer layer surface). The solution is heated to provide the superconductor material.
In general, the invention relates to methods of making superconductors (superconductor films formed from a precursor), reactors that can be used to make superconductors, and systems that contain such reactors. The methods, reactors and systems can be used to provide high quality superconductor materials, such as superconductor films formed from a precursor, (e.g., high quality rare earth-alkaline earth-copper oxide superconductor materials, such as YBCO) relatively quickly. For example, the methods, reactors and systems can be used to relatively quickly form superconductor materials (e.g., superconductor films formed from a precursor) having good crystallographic orientation (e.g., YBCO with c-axis out of plane and biaxial texture in-plane) and/or good superconductivity (e.g., critical current density of at least about 5xc3x97105 Amperes per square centimeter and/or critical current of at least about 100 Amperes per centimeter of width).
In one aspect, the invention features a method that includes providing a film containing barium fluoride on a surface of a substrate, and impinging a first reactant gas mixture on the film. The method also includes heating the substrate to a first temperature while impinging the first reactant gas on the film to provide a superconductor material on the surface of the substrate. The first reactant gas impinges on the film at an angle that is at least about 5xc2x0 relative to the surface of the substrate.
In another aspect, the invention features a method of forming a superconductor material. The method includes providing a film containing barium fluoride on a surface of a substrate to form a first article, and heating the first article while exposing the first article to a first gas environment within a first region of a reactor to form a superconductor material on the surface of the substrate, thereby forming a second article having the superconductor on the surface of the substrate. The method also includes moving the second article to a second region of the reactor, and exposing the second article to a second gas environment within the second region of the reactor so that substantially all the barium fluoride that was present in the film is converted to the superconductor material.
In another aspect, the invention features a method of making a superconductor material. The method includes impinging a reactant gas on a surface of a film containing barium fluoride to form the superconductor material. The superconductor material is supported by a surface of a substrate, and the superconductor material has a c-axis growth rate in a direction substantially perpendicular to the surface of the substrate that is at least about one xc3x85 per second.
In one aspect, the invention features a method of making a superconductor material. The method includes providing a film containing barium fluoride on a surface of a substrate, and impinging a reactant gas on a surface of the film to form the superconductor material on the surface of the substrate. A portion of the superconductor material located at a first point of a surface of the superconductor material has a first c-axis growth rate in a direction substantially perpendicular to the surface of the substrate. A portion of the superconductor material located at a second point of the surface of the superconductor material has a second c-axis growth rate in the direction substantially perpendicular to the substrate. The first c-axis growth rate in the direction substantially perpendicular to the substrate is substantially the same as the second c-axis growth rate in the direction substantially perpendicular to the substrate, and the first and second points of the surface of the superconductor material are at least about five centimeters apart.
In another aspect, the invention features a method of making a superconductor. The method includes providing a film containing barium fluoride on a surface of a substrate, and heating a reactant gas prior to contacting a surface of the film. The method also includes impinging the heated reactant gas on the surface of the film to form the superconductor.
In a further aspect, the invention features a reactor for forming a layer of a superconductor material. The reactor includes a housing, a barrier, at least one outlet, and a vacuum device. The housing is configured to hold a substrate for the layer of the superconductor material. The barrier is disposed in the interior of the housing configured to divide the interior of the housing into first and second regions. The barrier is formed of a substantially gas permeable member configured so that the first and second regions of the housing are in fluid communication. The at least one outlet is in the interior of the housing, and is configured so that, during operation when the substrate is present in the housing, a reactant gas can flow from the at least one outlet toward a surface of the substrate so that a film on the surface that contains barium fluoride can be converted to the layer of the superconductor material. The vacuum device is in fluid communication with the interior of the housing, the vacuum device being configured so that, during operation when the substrate is present in the housing, the vacuum device can remove one or more gases from a location adjacent the surface of the substrate.
In one aspect, the invention features a system for forming a layer of a superconductor material. The system includes a housing, a first gas source, a second gas source, a vacuum device, a first heater, and a second heater. The housing has first and second regions, and the housing is configured to hold a substrate for the layer of the superconductor material. The first gas source is in fluid communication with the first region of the housing so that a reactant gas can flow from the first gas source to an interior portion of the first region of the housing and so that, during operation when the substrate is present in the housing, the first reactant gas is directed toward the surface of the substrate. The second gas source is in fluid communication with the second region of the housing so that a second reactant gas can flow from the second gas source to an interior portion of the second region of the housing and so that, during operation when the substrate is present in the housing, the second reactant gas is directed toward the surface of the substrate. The vacuum device is in fluid communication with the interior of the housing, and the vacuum device is configured so that, during operation when the substrate is present in the housing, the vacuum device can remove one or more gases from a location adjacent the surface of the substrate. The first heater is adjacent the first region of the housing, and the first heater is configured to heat the first region of the housing during operation of the system. The second heater is adjacent the second region of the housing, and the second heater is configured to heat the second region of the housing during operation of the system.
In some embodiments, the invention can provide methods of making superconductor materials (e.g., superconductor films formed from a precursor) at a relatively high rate (e.g., c-axis growth rate of at least about one Angstrom per second in a direction substantially perpendicular to the surface of the substrate). The superconductor materials can have good critical current density, good critical current, and/or good crystallographic orientation.
In certain embodiments, the invention can provide methods of making superconductor materials (e.g. superconductor films formed from a precursor) in a relatively uniform manner. For example, the superconductor material can grow at a relatively uniform growth rate (e.g., along the c-axis in a direction substantially perpendicular to the surface of the substrate) at points on the surface that are relatively far removed (e.g., more than about five centimeters from each other in any given direction).
In some embodiments, the invention can provide methods of making superconductor materials (e.g., superconductor films formed from a precursor) with reduced formation of undesirable gas boundary layers at the surface (e.g., undesirable gas boundary layers of product gases).
In certain embodiments, the invention can provide methods of making superconductor materials (e.g. superconductor films formed from a precursor) while the surface is substantially unpreheated. For example, the reactant gas(es) can be pre-heated.
In some embodiments, the invention can provide methods of making superconductor materials (e.g., superconductor films formed from a precursor) that involve relatively uniform formation of the superconductor over relatively large areas.
In some embodiments, the invention can provide reactors that can be used in these and other methods.
In certain embodiments, the invention can provide a reactor that allows for relatively good reactant gas mixing.
In some embodiments, the invention can provide a reactor that allows for substantial removal of reactant gas(es).
Features, objects and advantages of the invention are in the description, drawings and claims.